Because of their relatively simple genetic structure when compared to other organisms. Not to mention, they breed in extremely high numbers which is great for scientists looking to do many trials, as most are. Their life cycle is also very short which means we can observe their entire life span and witness the effects of testing at all stages.
All are except the first one. Microfilaments are designed for support of cell structure.
Answer:
In 1973,
The maximum length for the beak of birds was obserbed to be less than 12mm in length
While, at 1978, it was observed that some birds had beak length at 12mm.
From 1973 to 1978, it can be observed that short beaks bird was more in population than 1978.